In recent years, there have been proposals for a power supply system that supplies electric power to be consumed in homes, shops/stores, business buildings, and the like by using not only electric power supplied from a power company (hereinafter, system electric power) but also electric power supplied by discharging a storage battery. A storage battery is charged in advance by consuming system electric power, and thereby, it is able to discharge to supply power at a desired timing. This makes it possible for a user of such a power supply system to change the timing of consuming the system electric power by controlling timings of charging and discharging the storage battery.
Generally, power companies charge a combination of a fixed basic charge and a metered charge for their system electric power. Besides, power companies are allowed to make contract with their customers to charge their customers the metered charge at different rates at different times of day. Thus, a customer under such a contract is able to reduce the electric power charge (metered charge) that he/she pays to a power company by using the above power supply system to charge the storage battery with electric power by consuming the system electric power when the rate of the metered charge is low, and to supply electric power by discharging the storage battery when the rate of the metered charge is high.
Furthermore, in the above contract, power companies often set the rate of the metered charge to be high at times of day when there is a large demand for system electric power, and to be low at times of day when the demand for system electric power is smaller. This is for the purpose of leveling out the demand for system electric power to thereby make it possible for power companies to realize efficient generation of system electric power. If power companies are able to efficiently generate system electric power (in particular, by thermal power generation), it is possible to reduce CO2 emission from the power generation. Thus, no matter what contract a customer has with a power company, it is preferable to the customer, from a viewpoint of reducing CO2 emission, to charge the storage battery when the demand for system electric power is small and to discharge the storage battery when the demand for system electric power is large.
Besides, as an example of such a power supply system that controls charging and discharging of a storage battery, for example, Patent Literature 1 listed below proposes an electric power supply system that performs simulation of charging and discharging of a storage battery, and charges and discharges the storage battery to reduce cost.